I'm a little late to this party, but I have some relevant info. I swapped a second gen SV650 shock onto my EX500 (pretty similar to the NewGen/300 suspension setup) for a while.
• It has a 430lb/in spring on it, compared to 525 on the NewGen (I understand the 300 to be the same). For comparison, the PreGen is 440 and the EX500 is only 300.
• The SV spring is larger OD, as you can see in the pic above. You'll probably need bowed links and/or spacers for adequate clearance, like the GSXR. All of the these little Ninja springs are smaller OD than "standard" shock springs found on aftermarket shocks and many other bikes.
• The SV shock is longer. The NewGen shock is already a bit longer than the EX500 shock, so I actually drilled a separate hole further up the clevis to match my OEM shock.
• As mentioned, the Suzuki shocks use 10mm mounting bolts while the Kaws use 12mm. I got a 12mm reamer bit and used a drill press to open up the holes. It ended up being a more snug (but still free-moving) fit than the OEM holes. The SV shock uses a threaded clevis rather than the bolt passing through to a separate nut, so there was a bit more material there to go through. The spacers that DannoXYZ mentioned above could replace modding the top eye.
• The SV clevis, like the GSXR clevis, is narrower than the Kaw lower mount. Whereas people file/machine the GSXR clevis wider, the cheap SV clevis can simply be pried open a little wider with some nuts and threaded rod (or some blunt force). In my case, with moving the mounting hole up closer to the top of the clevis, it rubbed on my mount a little bit, rather than moving completely freely. Just make sure that you have sufficient clearance, but it's a lot easier to modify than the more solid clevis on the GSXR shock.
The SV shock is a decent drop-in upgrade on the EX500. It's the right spring rate for a ~180lb rider, the required mods are easy to do in your average garage, and it's dirt cheap. However, it's nothing special. It's your standard budget bike, unserviceable, minimally-adjustable shock. If it didn't have a very desirable spring rate, I would see no reason to use it. If you can do a GSXR shock, that's more adjustable and serviceable for not too much more work.
The PreGen shock/spring will drop right in on the newer Ninjettes, and has a very similar spring rate. It lacks any preload adjustment though, and is a tad bit shorter. You can swap the PreGen spring onto an EX500 shock though. You'll need a spring compressor to get the spring off the PreGen shock, but the EX500's threaded preload adjuster means it comes apart easily (plus it offers more precise preload adjustment). The PreGen spring is a bit shorter, so you may need to add a spacer if you need a lot of preload. The shock seemed to be a little bit shorter than the NewGen/300 too, which may give you a bit of lowering without needing separate links.
I consider the SV and all the Ninjette shocks to be pretty basic with no/limited adjustment. I consider them resprings to get something that matches my weight, not a "shock upgrade" per se. In the end, I used the NewGen shock because it best matched my weight, and had the bonus of requiring no mods and lifting the rear a bit. The SV shock was easy to mod, but did still require several mods to fit properly. The PreGen spring swapped onto the EX500 shock gives the same spring rate, with no mods and pretty minimal work.
The GSXR shock requires more work to mod, and has more fitment issues (with spring size and the canister), but is a better shock all-around. The different years and bike sizes used different spring rates too. Based on
my research, the '01-'02 GSXR1000 should have the same spring rate as the SV, if you could use that part (cheap on eBay) instead, or even swap its spring onto the GSXR600 known to work on the Ninjette. The early SV and the GSXR600 commonly recommended both have spring rates similar to the stock shock, so it makes sense that they wouldn't really help you if you're trying to find a softer spring.